ZIF-67-derived N-CNT@CoMo-LDH core-shell nanocomposite for efficient alkaline electrocatalytic hydrogen evolution reaction

Hydrogen is an ideal safe and clean energy source, which can be produced by the electrocatalytic hydrogen evolution reaction (HER). The high overpotential of HER is one of bottlenecks for practical application, thus efficient and stable electrocatalysts, especially inexpensive electrocatalysts, are being vigorously developed to facilitate the reaction. Herein, we report the rational synthesis of a non-noble transition metal electrocatalyst via combined self-assembly and ion-exchange strategy. Zeolitic Imidazolate Framework-67 (ZIF-67) was in-situ grown on the surface of polypyrrole-derived nitrogen-doped carbon nanotubes (N-CNT) through a self-assembly method and then ZIF-67 was transformed into a CoMo layered double hydroxide (CoMo-LDH) through an ion-exchange reaction. As a result, a nanocomposite with N-CNT as the core and CoMo-LDH as the shell (N-CNT@CoMo-LDH) was successfully synthesized. The optimal N-CNT@CoMo-LDH exhibits excellent HER performance with a low overpotential of 86 mV at 10 mA cm −2 in 1 M KOH, superior to ZIF-67, CoMo-LDH, N-CNT@ZIF-67 and many reported LDH-based electrocatalysts. Additionally, the N-CNT@CoMo-LDH maintains approximately 86% of its initial current density after 24-h continuous test, with an overpotential increase of only 9 mV after 3000 cycles. The improved electrocatalytic HER performance is primarily attributed to the synergistic interaction between Mo 6+ and Co 2+ /Co 3+ , facilitating the formation of active sites, and N-CNT as core to enhance electron transport rates and inhibit the stacking of CoMo-LDH nanosheets, thus exposing more active sites of CoMo-LDH. Furthermore, its HER is confirmed to be the Volmer-Heyrovsky mechanism. This work provides a promising pathway for synthesizing highly efficient and stable electrocatalysts based on inexpensive non-noble metals.